Latent image forming film, latent image identifying kit and method for identifying latent image

Abstract

A latent image forming film comprising: a reflective layer; and a polarization converting and rotating layer placed on a surface of the reflective layer, the polarization converting and rotating layer changing an ellipticity of polarized incident light and concurrently rotating a polarization direction of the polarized incident light.

1 . A latent image forming film comprising:
 a reflective layer; and   a polarization converting and rotating layer placed on a surface of the reflective layer, the polarization converting and rotating layer changing an ellipticity of polarized incident light and concurrently rotating a polarization direction of the polarized incident light.   
     
     
         2 . The latent image forming film according to  claim 1 , wherein the polarization converting and rotating layer contains liquid crystal molecules fixed so as to have a twisted nematic orientation structure. 
     
     
         3 . The latent image forming film according to  claim 1 , wherein the polarization converting and rotating layer is a layer obtained by orienting a high-molecular-weight liquid crystal having a glass transition temperature of 70° C. or more so as to have a twisted nematic orientation in a liquid crystal state, and then by fixing the high-molecular-weight liquid crystal. 
     
     
         4 . The latent image forming film according to  claim 2 , wherein
 a helical pitch of a helical structure of the twisted nematic orientation structure is 2 μm or more, and   a number of pitches of the helical structure is less than 2.   
     
     
         5 . The latent image forming film according to  claim 1 , wherein
 an optical twist angle of the polarization converting and rotating layer ranges from 85 to 275°, and   an optical retardation of the polarization converting and rotating layer ranges from 450 to 700 nm.   
     
     
         6 . The latent image forming film according to  claim 1 , wherein
 an optical twist angle of the polarization converting and rotating layer ranges from 265 to 365°, and   an optical retardation of the polarization converting and rotating layer ranges from 750 to 1100 nm.   
     
     
         7 . A latent image identifying kit comprising:
 the latent image forming film according to  claim 1 ; and   an identification tool formed of a plurality of linear polarizing plates that have absorption axis directions different from each other.   
     
     
         8 . A method for identifying a latent image comprising the steps of:
 observing a plurality of wavelengths of light beams of a latent image, the plurality of wavelengths of light beams being observed through a plurality of linear polarizing plates which form an identification tool being placed on the latent image forming film according to  claim 1 , and which have absorption axis directions different from each other; and   identifying the latent image according to a combination of the wavelengths of the light beams of the latent image.